The web page for mini torii says that if you want more power "You can bridge these amps into mono blocks for twice the power if you have 8 or 16 ohm speakers." What does this mean exactly? Does it involve more equipment?

It means two Mini-Toriis. Each can be "bridged," that is both channels wired to one input, so in effect it beomes a mono amplifier. That way you would have one mono amplifier with more power for each channel. The "bridging" can be accomplished several ways and I don't think requires more than some wire/cable if done externally.